Why do naruto have to go for the FTG when naruto has better overall speed than that?
All S/T jutsus has the limitation that After teleporting behind or near the enemy, its user has to land his attack that relies on striking speed which hinders their overall speed.This provides an opening for the enemy to dodge or block the attack.
In the case of naruto, Naruto doesnt have that limitation that's why naruto successfully cut the arm of kaguya while sasuke wasn't able to do it.
FTG requires marking while naruto's raw speed doesn't.Ay, Bee, Yamato and Kakashi referred naruto's raw speed as fast as FTG.But if we add Striking speed with it then naruto's speed blitz is overall faster than FTG.
BTW if naruto have gotten FTG then it would be impossible for anyone to touch naruto.FTG + Naruto's speed blitz wiould be too OP